Temperature sensitive apparatus



July 4, 1961 'r. E. LARSEN 2,990,878

TEMPERATURE SENSITIVE APPARATUS Filed June 6, 1958 2 Sheets-Sheet 1 40 45 L U. If mar/04 cwrm Bx 27 a H 28 26+ 2 35 24 I9 25 x 1 l,'/// ,1", I, I, I,

INVENTOR. THEODORE E. LARSEN F W"- a M ATTORNEY July 4, 1961 T. E. LARSEN TEMPERATURE SENSITIVE APPARATUS 2 Sheets-Sheet 2 Filed June 6, 1958 BURNER MOTOR 0- IGNITION INVENTOR.

THEODORE E. LARSEN ATTORNEY United States Patent 9 i 2,990,878 TEMPERATURE SENSITIVE APPARATUS Theodore E. Larsen, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Filed June 6, 1958, Ser. No. 740,396 9 Claims. (Cl. 15828) This invention is concerned with an improved temperature sensitive apparatus and particularly with a temperature sensitive apparatus wherein a first and a second temperature responsive means maintains the first temperature responsive means insensitive to a temperature change until the common of the first and second means reaches a given value, whereupon the first temperature responsive means is free to respond to this temperature.

While the apparatus temperature of this application has a great variety of applications, it is shown in conjunction with a fuel burner primary control having a safety switch or lockout means, the primary control being used to supervise a fuel burner unit and thereby safeguard life and property in the event of improper operation of the fuel burner unit.

Specifically, the preferred modification of the present invention utilizes a relatively small flame sensing apparatus having integral switching mechanism in which the principal elements are a temperature sensitive bimetal, a temperature sensitive ferromagnetic armature and a slip friction clutch assembly. This apparatus is provided with a closed-cold switch and closed-hot switch. The closed-cold switch is closed when the burner unit is in the standby condition and the closed-hot switch is closed when a flame is present at the burner unit. It is necessary that the closed-cold switch be maintained in its closed position during standby condition of the burner since the electrical circuitry of the primary control with which the flame sensing apparatus is utilized requires that this switch be closed in order to start the fuel burner unit. Furthermore, this flame sensing apparatus must be capable of fast response to the presence of flame and must therefore open the closed-cold switch and close the closed-hot switch a relatively short time after the flame has been established at the fuel burner unit.

These requirements are such that the flame sensing element must be capable of responding rapidly when a flame appears but must likewise be able to differentiate between this flame condition and a condition leading to a temperature change, such as a marked change in ambient temperature. In the preferred modification of the present invention, the'flarne sensing element utilizes a temperature responsive bi-metal which is the primary sensing element and this bi-metal member by itself has a response suflicient to open the closed-cold switch in as little as a F. change. Since the primary control will not allow the burner unit operation to start unless the closed-cold switch is closed, ambient temperature changes of 20 F. would, without the construction of the present invention, result in numerous nuisance shut downs.

Furthermore, while the bi-metal element of this de vice responds to as little as a 20 F. temperature change, the over all change in temperature experienced during an operating cycle is much greater than this 20 F. range and therefore a slip friction clutch mechanism must be provided to prevent damaging stress being set up within the structure of the bi-metal element. As is well known, a slip friction clutch mechanism of this type allows a certain pressureto be built up by the free end of a bi metal and once this pressure or force is built up, the remaining force exerted by subsequent heating of the Patented July 4, 1961 bi-metal is absorbed by the movement of the slip friction clutch mechanism.

Specifically, the preferred modification of the present invention provides a base structure on which a temperature sensitive bi-metal element is mounted by means of a slip friction connection. The base member likewise mounts a pair of switch members and a magnet. This magnet cooperates with a ferromagnetic armature mounted on the free end of the bi-metal element to thereby bias this bi-metal element and maintain the closed-cold switch in its closed condition. Upon the temperature sensitive bi-metal and its Curie point armature being subjected to a temperature rise, the bi-metal tends to open the closed-cold switch. However, the magnet maintains this switch in a closed condition due to the attraction of the ferro-magnetic armature. As the temperature of the bi-metal and its armature continues to increase, the ferromagnetic armature decreases in permeability to the point where the force built up by the expanding bi-metal exceeds the magnetic attraction between the magnet and the ferromagnetic armature. When this occurs, the bi-metal element is free to cause the switches to be actuated.

It is an object of the present invention to provide a temperature sensitive apparatus comprising a support member on which a temperature sensitive bi-metal is mounted and in which biasing means are provided associated with the bi-metal and including a magnet and a ferromagnetic armature biasing the movcable portion of the bi-metal to a first position to thereby restrict movement of the movcable portion of the bi-metal until the temperature of the bi-metal and the ferromagnetic armature reaches a given value.

It is a further object of the present invention to provide a temperature sensitive apparatus having thermal responsive means including means movcable in response to a temperature change and likewise including thermal magnetic means associated with the thermal responsive means in a manner to restrict movement of the moveable means until the temperature of the thermal magnetic means reaches a given value.

The constiuction of the present invention wherein the range of temperatures to which the bi-metal is responsive may be controlled, results in a burner control system wherein the differential of the flame sensing element may be adjusted to be very small since this differential need not be large enough to accommodate a possible change in ambient temperature. In other words, with the construction of the present invention, the differential in operating temperature of the flame sensing element may now be lower than the actual expected changw in ambient temperature due to the fact that the flame sensing element is not sensitive to these changes in ambient temperature since the ferromagnetic armature and the magnet maintain the closed-cold switch in a closed condition until a given temperature is reached, this given temperature being above the maximum ambient temperature to be experienced. The improved temperature sensitive apparatus thereby provides a burner control system utilizing a safety lock-out means wherein the safety lock-out means may have a relatively fast timing function since upon flame being established, the flame detector which is connected in controlling relationship to the safety lock-out means, responds very quickly to the presence of flame and thereby renders the safety lock-out means ineffective to perform the lock-out function.

It is therefore a further object of the present invention to provide an 'miproved burner control system for use with a fuel burner wherein a control relay is provided to energize the burner unit and wherein safety lock-out means are provided, the control relay and safety lock-out means being controlled by a flame detector having a normal-ly closed and a normally open switch and including a first temperature responsive means which is associated with a second temperature responsive means such that the first temperature responsive means maintains the normally closed switch in a closed condition until the first and second temperature responsive means are subjected to a given minimum temperature, whereupon the first temperature responsive means is effective to cause the closed switch to open and to cause the open switch to close, and wherein start circuit means are provided for the relay including the normally closed switch and running circuit means are provided for the relay including the normally open switch.

These and other objects of the present invention will be apparent upon reference to the following specification, claims and drawing, of which FIGURE 1 is a showing of the improved temperature sensitive apparatus mounted on the oil pipe of a gun type oil burner, showing a portion of the blast tube housing broken away,

FIGURE 2 is a view of the temperature sensitive apparatus showing a portion of the case thereof broken away,

FIGURE 3 is a showing of the electrical terminal portion of the temperature sensitive apparatus, showing the mounting bracket therefor,

FIGURE 4 is an end view of the temperature sensitive apparatus, showing the apparatus with a portion of the housing thereof removed,

FIGURE 5 is a showing of a further modification of the prment invention, and

FIGURE 6 is a showing of an improved burner control system using the temperature sensitive apparatus.

Referring specifically to FIGURE 1, the reference numeral 10 designates the blast tube of a gun type oil burner, a portion of the blast tube being broken away to show the oil line 11 and the oil nozzle 12. The oil line 11 is supported by means of a support 13 which like' wise mounts a pair of ignition electrodes 14 and 15, these ignition electrodes being disposed in igniting relation to the nozzle 12. The reference numeral 16 identifies the improved temperature sensitive apparatus of the present invention. It can be seen that this apparatus is mounted in viewing relation to the flame which may be present at the nozzle 12 and that the apparatus 16 is thereby arranged to detect the presence or absence of flame at the fuel burner unit including the gun type oil burner.

Referring now to FIGURE 2, the temperature sensitive apparatus 16 is shown with portions thereof in section. The reference numeral 17 designates a viewing window, preferably lime glass. The reference numeral 18 designates a box shaped wall member constructed preferably of a ceramic material. The reference numeral 19 designates a base assembly which is likewise constructed of a ceramic material. The members 18 and 19 are joined together, for example by means of a fine glass frit which is painted on the mating surface of the members 18 and 19, the members 18 and 19 then being heated to a high temperature, thereby causing the glass frit to melt and seal the members 18 and 19 together. Furthermore, the glass member 17 is sealed to the member 18, thereby completing a hermetically sealed housing for the temperature sensitive apparatus included therein.

Electrical contact to the apparatus contained within the housing is achieved by means of three electrical terminals 20, 21 and 22. These terminals are inserted through openings provided in the base member 19 and are attached to the metallic members 23, 24 and 25 by means of a rivet or butt welding type fastening.

The reference numeral 26 designates a first temperature means in the form of a bi-metal element having a free end at the left-hand end thereof and having the right-hand end thereof mounted with respect to the base member 19 by means of a slip friction clutch mechanism identified by the reference numeral 27. This slip friction clutch arrangement 27 may take a variety of forms, and for purposes of convenience is disclosed as the arrangement of the co-pending Carl J. Bishofberger application, Serial No. 713,476, filed February 5, 1958, now Patent 2,882,371. This application may be referred to for a complete explanation of the operation of the slip friction clutch mechanism 27. For the purposes of the present explanation, it suifices to say that upon the bi-metal element experiencing a temperature change, the free end thereof moves until its movement becomes restricted by switch members, to be later explained. Upon further temperature change being experienced by the bi-metal 26, a given contact pressure or force is built up by the free end of the bi-metal, this force being determined by the construction of the slip friction mechanism 27. Upon a still greater temperature change being experienced by the bi-metal 26, the contact pressure or force exerted by the free end thereof remains constant and the right-hand end mounted on the base member by means of a slip friction clutch member 27, moves to absorb the additional movement of the bi-metal 26 caused by this still greater temperature change.

The reference numeral 28 of FIGURE 2 designates a ferromagnetic armature. The ferromagnetic armature is constructed of a material whose permeability changes with temperature. This member 28 is a Curie point material whose magnetic characteristics change with temperature. Specifically, the member 28 loses its magnetic properties when heated above a critical temperature, this being the Curie point temperature of the material. As an example, the member 28 may be formed of an alloy of iron and nickel. The Curie point armature 28 can therefore be identified as a second temperature responsive means or a thermo magnetic means, this means being mounted on the free or moveable portion of the first temperature responsive means, that is bi-metal 26. The moveable end of the bi-metal 26 likewise controls switch means having the contact members 29, 31 and 35. With the apparatus as shown in FIGURE 2, the bi-metal 26 is in its cold position and moveable contact 29 is in engagement with stationary contact 31. As can be seen more clearly in FIGURE 4, the contact 31 is mounted in the center of a doughnut shaped magnet 32, the magnet 32 being mounted on the upper portion of the U-shaped member 23. Referring to FIGURE 4, it can be seen that member 23 is provided with a pair of extending arms 33 and 34 which connect the upper and lower portions of this U-shaped member.

As mentioned, the apparatus of FIGURE 2 is shown in the cold position. In this position, the magnet 32 exerts a force upon the armature 28 and maintains the contact 29 in its engagement with contact 31, thereby maintaining the closed-cold switch in the closed position. A subsequent temperature rise which may be experienced by the uni-t of FIGURE 2 due, for example, to a change in ambient temperature, tends to cause the free end of the bimetal 26 to move in a downward direction to thereby break the closed-cold switch. However, the ambient temperature ranges to be experienced by this device are such that the magnet 32 at all times exerts a force upon the armature 28 and thereby maintains the switch 2931 in a closed condition. Likewise, any vibration, such as by the initial installation of the gun type oil burner of FIG- URE 1, does not cause the switch 2931 toopen due to the force exerted upon the armature 28 by the magnet 32.

Upon a flame being established at the nozzle 12 of FIG- URE 1, the radiant heat energy present in the flame passes through the glass member 17 and heats the bi-metal 26 as well as the ferromagnetic armature 28. The magnetic properties of the armature decrease until its Curie point is reached, whereupon the magnet '32 no longer exerts a force on the armature to maintain the switch 29-31 in a closed condition. The bi-metal 26 has simultaneously been heated by the radiant heat energy of the flame and has as a result begun to build up a force in opposition to the magnetic attraction present below the Curie temperature. At the point where this bi-metal force exceeds the magnetic attraction between armature 28 and magnet 32, the free end of the bi-metal, that is the lefthand end, moves in a downward direction to cause its moveable contact 29 to move into engagement with stationary contact 35. This point is a function of the magnetic permeability of the armature and the force required to move the slip-friction mechanism, and could conceivably be adjusted to any value. This moveable contact 29 and the stationary contact 35 comprise the closed-hot switch of the apparatus. Furthermore, the movement of the free end of the bi-metal 26 causes the closed-cold switch 29-31 to move to an open condition.

From the above explanation'it can be seen that an improved temperature sensitive apparatus is provided wherein a first temperature responsive means, in the form of bi-metal 26, is biased to a first position wherein a switch 29-31 is closed, this biasing being accomplished by means of a second temperature responsive means in the form of magnet 32 and Curie point armature 28. Furthermore, it can be seen that the first temperature responsive means is rendered insensitive or is non-responsive to a temperature change which would normally cause the free end thereof to move, this temperature being a function of the Curie point temperature of the armature 28. Upon the armature 28 being heated to this Curie point temperature, and upon a simultaneous temperature rise equivalent to that which would normally cause the free end of the bi-metal to move, the bi-metal is free to move to cause the switch 29-35 to close. It should be remembered that while the temperature of the bi-rnetal 26 is increasing, so long as the temperature of the Curie point armature 28 lies below its critical temperature, the flexing or movement of the bi-metal 26 may be either counterbalanced up to a point by the attraction of the magnet for the armature or may be absorbed by movement of the slip friction clutch mechanism 27, such that upon the critical temperature of armature 28 being reached, a further temperature rise is necessary to cause the free end of the bi metal 26 to move to control switch 29-35 and switch 29-31.

Referring now specifically to FIGURE 3, the mounting bracket for the improved temperature sensitive apparatus is shown. This mounting bracket is preferably constructed of a metal and is provided with a C-s-haped bracket 36 mounting a bolt 37 which is adapted to engage the oil line 11 of FIGURE 1. Furthermore, this mounting bracket is provided with a U-shaped portion 38, which partially encircles the terminal members 20-22. Furthermore, this U-shaped member is provided with a pair of extending arms 40 and 41 which mate with channels 42 and 43 provided in the housing members 18 and 19. As can be seen more clearly in FIGURE 2, the members 40 and 41 are provided with ear portions 45 and 46 which rigid-1y hold the temperature sensitive apparatus in relation to the oil tube 11 and the nozzle 12.

Referring now to FIGURE 5, this figure shows a further modification of the present invention, showing a bi-metal 47 which mounts a moveable contact 48. This bi-metal member 47 is mounted in relation to a base member 49 by means of a slip friction clutch member, for example the member 27 of FIGURE 2. The base member 49 also mounts an electrical terminal 50 which makes electrical contact to a stationary contact 51 which is mounted in the center of a doughnut shaped magnet 52. The magnet 52 is positioned in relation to a Curie point member 53, the Curie point member 53 being formed in a generally cup shaped fashion to partially encircle the doughnut shaped magnet 52. For purposes of simplicity, the apparatus of FIGURE 5 shows only a closed-cold switch 48-51. Furthermore, the electrical terminal similar to terminal 50 which makes electrical contact to bi-metal 47 is not shown and the slip friction member mounting the righthand end of the bi-metal 47 to base 49 is not shown. The

apparatus of FIGURE 5 functions in much the same manner as the apparatus of FIGURE 2 in that bi-metal 47 is held in its cold position by means of the magnet 52 having in essence a pair of pole faces 54 and 55 formed as extending ears of the Curie point member 53. The bimetal 47 of FIGURE 5 differs from the bi-metal 26 of FIGURE 2 in that the bi-metal 47 moves in an upward direction upon an increasing temperature. However, until the temperature of the Curie point member 53 reaches the critical temperature, which is related to the Curie point temperature, the bi-metal 47 is held by magnetic attraction such that the switch 48-51 is maintained in the closed position. Upon this critical temperature being reached,- the free end of bi-metal 47 is free to move in an upward direction to open switch 48-51. The essential difference between the modification of FIGURE 5 and that of FIGURE 2 is that in FIGURE 5 the Curie point armature 53 is rigidly attached to the base member 49 whereas in FIGURE 2 the Curie point armature 28 is mounted on the free end of the bi-metal 26.

Referring now specifically to FIGURE 6, an improved burner control system is shown utilizing the improved temperature sensitive apparatus of FIGURE 2, recognizing that the modification of FIGURE 5, wherein a closedhot switch is provided, could likewise be used. A primary burner control is designated as contained within broken lines 60. This primary burner control is adapted to be mounted on the gun type oil burner of FIGURE 1 and is adapted to control the ignition 61 and the burner motor 62 thereof. Furthermore, the flame at the nozzle 12 is supervised or monitored by the temperature responsive apparatus or flame detector 16. In FIGURE 6, the flame detector 16 is shown in schematic form the cold closed switch being shown as member 29-31 and the hot-closed switch shown as the members 29-35. The overall control of the fuel burner unit is achieved by means of a means responsive to the need for operation of the fuel burner unit in the form of a thermostat 64. Thermostat 64 is of the heat anticipating type having an anticipating heater 65.

The primary control 60 includes a main control relay 66 having a tapped winding 67 and switch blades 68, 69 and 70 controlled thereby. The relay 66 is shown in its de-energized position and upon energization of winding 67, the switch blade moves into engagement with the stationary contacts 71, 72 and 73.

Also contained within the primary control is a safety cut-out 74 having an actuating heater 75, a bi-metal 76 and a normally closed switch 77. This safety switch is of a conventional type and upon heating of the bi-metal 76, the upper portion thereof moves to the right thereby allowing switch 77 to assume an open position. In order to reset the safety switch, the reset button 78 is depressed, thereby allowing the switch 77 to assume its closed position as shown in FIGURE 6.

A second timer in the form of an ignition timer 79 is likewise provided in the primary control. This timer 79 is provided with an actuating heater 80 and a bi-metal 81, the bi-metal being coupled to an insulating member 82 which mounts moveable contacts 83 and 84. This timer is shown in its cold position and in this position the moveable contacts 83 and 84 engage the stationary contacts 85 and 86 respectively. Upon heating of the bi-metal 81, the bi-metal moves to the right such that the switches 83-85 and 84-86 are opened.

The operating voltage for the apparatus of FIGURE 6 is derived from an alternating voltage source, not shown, which is connected to power line conductors 87 and 88. Conductors 87 and 88 connect to the primary winding 89 of a transformer 90 and having a secondary winding 91. Furthermore, the power line conductors 87 and 88 connect to further conductors 92 and 93 which are connected to the ignition means 61 and the burner motor 62 of the gun type oil burner.

Referring now to the operation of the burner control system in FIGURE 6, upon a need for operation of the gun type oil burner, the thermostat 64 closes its switch. This establishes a starting circuit for the winding 67 of relay 66. This starting circuit can be traced from the left-hand terminal of secondary 91 through conductor 94, safety switch 77, conductor 95, the first portion of the winding 67, conductor 96, heater 75, conductor 97, temperature sensitive apparatus switch 29-31, conductors 98 and 99, start switch 83-85, conductor 100, heater 65, thermostat 64 and conductor 101 to the righthand terminal of secondary winding 91. From this circuit it can be seen that the winding 67 of relay 66 can be energized only if the safety switch 77 is in a closed position, if the heater 75 has electrical continuity, if the flame detector closed-cold switch 2931 is closed, and if the ignition timer 79 is in its cold position such that the start switch 8385 is closed. Energization of relay 66 causes the moveable switch blades 68, 69 and 70 to move into engagement with the stationary contacts 71, 72 and 73. The engagement of moveable switch blade 68 with contact 71 places the second portion of winding 67 in series with the heater 80 of ignition timer 79 and this series connection in parallel with the heater 75 of safety switch 74. The impedances of the heaters 75 and 80 and the number of turns in the second portion of the winding 67 are so proportioned that at this time the safety switch heater 75 is operatively energized while the ignition timer heater 80 remains operatively de-energized.

Upon switch blade 69 moving into engagement with contact 72, an energizing circuit is completed for the burner motor 62 and the ignition means 61. This can be seen by tracing a circuit from the power line conductor 87 through conductor 92, burner motor 62 in parallel with ignition means 61 and the ignition switch 84--86, conductor 102, switch 69--72, and conductor 93 to the other power line conductor 88. Therefore, the burner motor and the ignition means of the gun type oil burner are energized and the flame is normally established at the nozzle 12 of FIGURE 1.

As explained in connection with FIGURES 1 and 2, the radiant heat energy produced by this flame passes through the window 17 and heats the bi-metal 26 and Curie point armature 28. However, the closed-cold switch 2931 of FIGURE 2 or FIGURE 6, remains in a closed position until the Curie point armature 28 is raised to its critical temperature, at which point the magnet 32 is no longer able to maintain the free end of the bi-metal 26 in the cold position. Thereupon, a further temperature rise causes the bi-metal 26 to move in a downward direction, opening the switch 29-31 and closing the switch 2935. Referencing this description to FIGURE 6, the switch 2931 opens and the switch 29-35 closes. Upon the opening of the switch 29-31, the above mentioned starting circuit is opened, thereby de-energizing the heater 75 of the safety switch 74. The closing of switch 2935 completes a running circuit for the winding 67 of relay 66. This running circuit can be traced from the left-hand terminal of secondary winding 91 through conductor 94, switch 77, conductor 95, relay winding 67, conductor 105, switch 71-68, conductor 106, ignition timer heater 80, conductors 107 and 98, switch 29-415, conductor 108, switch 7073, conductor 109, anticipating heater 65, thermostat 64 and conductor 101 to the right-hand terminal of secondary winding 91. From this above traced circuit, it can be seen that upon the flame detector 16 detecting the presence of flame at the nozzle 12, the safety switch 74 is rendered inoperative and a running circuit is established for relay 66 which operatively energizes the heater 80 of ignition timer 79. After a time period, the ignition timer 79 causes these switches 83-85 and 84--86 to assume an open condition. This opens the initial starting circuit for relay 66 and also de-energizes the ignition means 61. From the above it can be seen that an improved burner control system has been provided utilizing the improved condition sensing "means wherein a safety switch 74 may be provided having a very short timing function, this very short timing function being controlled by the improved condition sensing means.

Other modifications of the present invention will be apparent to those skilled in the art and it is intended that the scope of the present invention be limited solely by the scope of the appended claims.

I claim as my invention:

1. Temperature sensitive apparatus comprising; dif ferential temperature responsive means subjected to a force tending to move it from -a first-to a second position upon said differential temperature responsive means experiencing a change in temperature through a given temperature differential, said differential temperature responsive means being constructed and arranged to normally move from said first to said second position independent of the absolute temperature at which said change in temperature occurs, absolute temperature responsive means cooperating with said differential temperature responsive means and constructed and arranged to maintain said differential responsive means in said first position until the absolute temperature experienced by said differential and said absolute temperature responsive means reaches a given absolute value, said absolute temperature responsive means then being ineffective to maintain said differential temperature responsive means in said first position and said differential temperature responsive means then being free to move from said first to said second position as the absolute temperature changes through said given temperature differential from said given absolute value of temperature at which said absolute temperature responsive means is ineffective, and control means controlled by said differential temperature responsive means as a result of said movement.

2. Temperature sensitive apparatus comprising; a support member, a temperature sensitive bi-metal mounted in relation to said support member and having a movable portion arranged to be subjected to a force tending to move it upon said bi-metal experiencing a temperature change, said movable portion being normally free to move due to said temperature change independent of the absolute temperature at which said temperature change occurs, biasing means associated with said bi-metal and including a magnet and a ferromagnetic armature biasing the movable portion of said bi-metal to a first position, said ferromagnetic armature being temperature responsive such that it loses its magnetic property when the absolute temperature thereof reaches a given value, to thereby restrict movement of the movable portion of said bi-metal until the absolute temperature thereof reaches said given value, whereupon said bi-metal may move from said first position due to said force as the temperature thereof continues to change, and switch means actuated as a result of the movement of said bimetal.

3. Temperature sensitive apparatus comprising; thermal responsive means including movable means subjected to a force tending to move it in response to a temperature change, said thermal responsive means normally being free to move upon experiencing said temperature change regardless of the absolute temperature at which said change takes place; thermal magnetic means associated with said thermal responsive means in a manner to prevent movement of said movable means until the absolute temperature of said thermal responsive means and said thermal magnetic means has reached a given value, thereupon said movable means is free to move as the absolute temperature thereof continues to change from said given value; and control means controlled as a result of the movement of said movable means.

4. Temperature sensitive apparatus comprising; a support member, a bimetal member, a slip friction clutch, means movably mounting a first portion of said bi-metal member on said support member by means of said slip friction clutch, said bi-metal member having a second portion which is normally free to move relative to said support member upon said bi-metal member experiencing a temperature change, said slip friction clutch functioning to allow movement of the first portion of said bi-met-al member when the second portion of said bi-metal member is prevented from moving, a ferrogmagnetic armature mounted on the second portion of said bi-metal member, a magnet mounted on said support member and cooperating with said ferromagnetic armatureto bias the second portion of said bi-metal member in the direction in which the second portion tends to move when said bi-metal member is subjected to a temperature fall, said ferromagnetic armature having a characteristic permeability which changes with temperature such that movement of the second portion of said bi-metal member is prevented until the temperature of said bi-metal and said ferromagnetic has been increased to a given temperature whereupon the permeability of said ferromagnetic armature is changed to the extent that said magnet no longer is effective to prevent movement of the second portion of said bi-metal member, the second portion of said bimetal member thereafter being free to move as a result of a subsequent temperature increase, and switch means controlled by the second portion of said bi-metal.

5. Temperature sensitive apparatus comprising; a base member, a first and a second stationary contact mounted on said base member in spaced relationship, a bi-metal member, slip friction means mounting a first portion of said bi-metal member to said base member, a Curie point armature and a movable contact mounted on a second portion of said bi-metal member such that said movable contact cooperates with said first and second contacts, the second portion of said bi-metal member being normally free to move between said first and second contacts as a result of a change in temperature of said bimetal member and said slip friction means being effective to allow movement of the first portion of said bi-metal member when the second portion of said bi-metal member is prevented from moving, a magnet, means mounting said magnet adjacent one of said stationary contacts to thereby magnetically attract said Curie point armature and bias said movable contact to engage said one stationary contact, said bi-metal member thereafter tending to cause movement of said movable contact out of engagement with said one stationary contact and into engagement with the other of said stationary contacts upon a temperature rise occurring, the Curie point characteristics of said armature being such that said bi-metal member is ineffective to move said movable contact until the temperature has risen above the critical temperature of said armature, said slip friction means being effective to allow movement of the first portion of said bi-metal member during this temperature rise, and said bi-metal member being effective to move said movable contact out of engagement with said one stationary contact and into engagement with the other of said stationary contacts as a result of a still further temperature rise.

6. Temperature sensitive apparatus comprising; a base member, a pair of stationary contacts mounted on said base member in spaced relationship, a bi-metal member, slip friction means, means mounting one end of said bimetal member on said base member by means of said slip friction means so that the other end of said bi-metal member extends generally between said stationary contacts, a movable contact and a Curie point armature mounted on said other end of said bi-metal member, said bi-metal member being effective upon experiencing a temperature change to cause movement of said other end of said bi-metal member until said movable contact engages a stationary contact, after which a further temperature change causes movement of said one end by virtue of said slip friction means, and a magnet mounted 'in the vicinity of one of said stationary contacts so as to magnetically attract said Curie point armature thereto and maintain said'movable contact in engagement with said one stationary contact, said bi-metal member being ineffective to cause said movable contact to disengage said one stationary contact and move into engagement with the other of said stationary contacts upon said bi-metal member experiencing an initial temperature rise, during which temperature rise said Curie point armature loses its permeability and after a sufiicient temperature rise has occurred said magnet no longer attracts said Curie point armature, said movable contact then being free to disengage said one stationary contact and move into engagement with said other stationary contact upon a further temperature rise.

7. A burner control system for use with a fuel burner, comprising; a control having an electrically energizable actuator and switch means controlled thereby and adapted to be connected to the fuel burner to cause energization thereof upon said actuator being energized, safety lockout means having an electrically energizable actuator and a normally closed lockout switch, a flame detector arranged to be subject to flame at the fuel burner unit and having a first temperature responsive means and a normally closed and a normally open switch controlled by said first temperature responsive means to normally be actuated respectively to open and closed conditions upon said first temperature responsive means experiencing a temperature change regardless of the absolute temperature at which said change takes place, second temperature responsive means arranged in controlling relation to said first temperature means to maintain said flame detector normally closed switch in a closed condition until said first and second temperature responsive means are subjected to a given minimum absolute temperature, whereupon said first temperature responsive means is thereafter effective to cause said flame detector normally closed switch to open and to cause said flame detector normally open switch to close upon an additional temperature change occurring after said given temperature is reached, starting circuit means for said control actuator including a source of voltage, said lockout actuator, said normally closed lockout switch, and said flame detector normally closed switch, and running circuit means for said control actuator including said flame detector normally open switch.

8. Temperature sensitive apparatus comprising; a bimetal element, support means, slip friction means mounting a first portion of said bi-metal element on said support means, a second portion of said bi-metal element thereby being subjected to a force tending to move it in a given direction when said bi-metal element is subjected to an increasing magnitude temperature change regardless of the absolute temperature at which said change takes place, thermal magnetic biasing means mounted with respect to the second portion of the bi-metal element and effective to bias the second portion of said bi-metal element against movement until the absolute temperature of said thermal magnetic biasing means reaches a given value, whereupon the second portion of said bi-metal element is then free to move in response to a further increase in temperature above said given value, and switch means controlled by the second portion of said bi-metal.

9. Temperature sensitive apparatus comprising; a base member, a temperature responsive bi-metal member, slip friction means mounting one end of said bi-metal member on said base member such that the other end of said bi-metal member is subjected to a force tending to move it with respect to said base member as said bi-metal member is subjected to an increasing magnitude temperature change regardless of the absolute temperature at which said change takes place, a Curie point thermo-magnetic member whose permeability undergoes a change when said thermo-magnetic member reaches a given absolute temperature, means mounting said thermo-magnetic member at said other end of said bi-metal member, a magnet, means mounting said magnet relative to said base member and in alignment with said thermo-magnetic member such that below said givenabsolute temperature said other end of said bi-metal is biased in the direction of said magnet, and upon said bi-metal and thermo-rnagnetic member being subjected to said given absolute temperature, said other end of said bi-metal is thereafter free to move as it experiences a subsequent increasing magnitude temperature change above said given absolute temperature, and switch means controlled by said other end of said bi-metal.

References Cited in the file of this patent UNITED STATES PATENTS Cubitt Q. Dec. 5, 1911 Beveridge Feb. 27, 1940 Klapperich Sept. 17, 1940 Wittman Dec. 31, 1940 Mantz Dec. 1, 1942 McCabe Jan. 1, 1957 Matthews Apr. 16, 1957 

